1. Field of the Invention
The present invention relates to a cryoablation catheter, and more particularly to a cryoablation catheter for creating long lesions.
2. Description of the Prior Art
Many medical procedures are performed using minimally invasive surgical techniques wherein one or more slender implements are inserted through one or more small incisions into a patient""s body. With respect to ablation, the surgical implement may include a rigid or flexible structure having an ablation device at or near its distal end that is placed adjacent to the tissue to be ablated. Radio frequency energy, microwave energy, laser energy, extreme heat, and extreme cold may be provided by the ablation device to destroy the tissue.
With respect to cardiac procedures, cardiac arrhythmia may be treated through selective ablation of cardiac tissue to eliminate the source of the arrhythmia. A popular minimally invasive procedure, radio frequency (RF) catheter ablation, includes a preliminary step of conventional mapping followed by the creation of one or more ablated regions (lesions) in the cardiac tissue using RF energy. Multiple lesions are frequently required. Often, five lesions, and sometimes as many as twenty lesions may be required before a successful result is attained. Sometimes only one of the lesions is actually effective.
Deficiencies of radio frequency ablation devices and techniques have been to some extent overcome by cryogenic mapping and ablation. Such cryogenic mapping techniques are in U.S. Pat. Nos. 5,423,807; 5,281,213 and 5,281,215. However, even though combined cryogenic mapping and ablation devices often times permit greater certainty and less tissue damage than RF devices and techniques, both cryogenic and RF ablation devices are usually configured for spot or circular tissue ablation.
Spot tissue ablation is acceptable for certain procedures. However, other procedures may be more therapeutically effective if multiple spot lesions are made along a predetermined line, or a single elongate or linear lesion is created in a single ablative step. Radio frequency ablation devices are known to be able to create linear lesions by dragging the ablation tip along a line while the ablation electrode is energized. U.S. patent application Ser. No. 09/518,044 entitled, xe2x80x9cCryoablation Catheter For Long Lesion Ablations,xe2x80x9d assigned to the same assignee as the present invention disclosing the concept of xe2x80x9cdraggingxe2x80x9d the ablation tip, or the cooling tip, of a cryoablation catheter along a line in order to create a long lesion. In order to accomplish this function, the cryogenic cooling nozzle is moved longitudinally along the inside of a cooling chamber to thereby cause the outer surface of the cooling chamber to be cooled along a linear path which in turn creates a linear lesion along the path.
In accordance with one aspect of the present invention there is provided a cryoablation catheter system for creating linear lesions which includes an outer tubular member capable of insertion into the vessels of the body, a ceiling cap disposed at the distal end of the outer tubular member for forming a cooling chamber at the distal end of the tubular member, an inner tubular member slidably disposed within the outer tubular member. The proximal end of the inner tubular member is adapted to receive a fluid, such as nitrous oxide. A fluid expansion nozzle, such as a Joule-Thompson nozzle, is disposed on the distal end of the inner tubular member. The catheter system also includes a nozzle control system which is comprised of an inner ring member formed of a magnetic material which is mounted on the proximal end of the inner tubular member, and an outer ring member formed of magnetic material which is slidably mounted on the outer tubular member. Because of the magnetic attraction between these two magnetic members, when the outer ring member is moved along the outer tubular member it xe2x80x9cpullsxe2x80x9d or draws the inner magnetic ring member along with the outer magnetic ring member to thereby cause the inner tubular member to be moved longitudinally which in turn causes the fluid expansion nozzle to be moved longitudinally within the cooling chamber.
In accordance with another aspect of the present invention, the inner tubular member is disposed coaxially within the outer tubular member so as to define a passageway between the inner tubular member and the outer tubular member, and a cylindrical support member is disposed between the inner tubular member and the outer tubular member for supporting the inner tubular member for movement within the cooling chamber. The cylindrical support member includes at least one passageway which extends through the support member to permit fluid, such as, nitrous oxide, to be returned through the passageway for removal from the catheter system. In accordance with still another aspect of the present invention, the inner magnetic ring member is disposed coaxially within the outer tubular member and extends in the passageway between the inner tubular member and the outer tubular member, and includes at least one passageway which extends through the inner magnetic ring member to permit fluid to be returned through the passageway for removal from the catheter. In accordance with still another aspect of the present invention, the fluid expansion nozzle takes the form of a Joule-Thompson nozzle which is disposed on the distal end of the inner tubular member.
With the nozzle control system of the present invention, it is possible to provide a cryoablation catheter system for creating linear lesions by moving the fluid expansion nozzle in a longitudinal direction along the interior of the cooling chamber while maintaining an entirely sealed catheter system. In other words, by use of magnetic attraction which exists from an external ring magnet and an internal ring magnet it is possible to xe2x80x9cpullxe2x80x9d the fluid expansion nozzle along a longitudinal path within the sealed cooling chamber while maintaining a hermetically sealed catheter system.
These and other objects of the present invention will become more apparent when considered in view of the following description of a preferred embodiment of the present invention.